Method for opaquing visible and infrared radiance and smoke-producing ammunition which implements this method

ABSTRACT

The invention concerns a method and a smoke-producing pyrotechnical ammunition to shield the visible and infrared radiance in a wave length included between 0.4 and 14 μm emitted by a target. First we produce instantly a first hot aerosol with a fast pyrotechnical composition, which masks the target through diffusion in the visible spectrum and with its emitting potential in the infrared zone. Then, we produce a second aerosol which contains hot carbon particles of which the size is included between 1 and 14 μm with a slow pyrotechnical composition for shielding mainly through diffraction the thermal image emitted by the target. The fast composition includes zinc and zinc oxide, potassium perchlorate, hexachlorobenzene or hexachloroethane powder and a binding agent. The slow composition includes a compound which generates carbon particles of 1 to 14 μm such as hexachlorobenzene hexachloroethane, naphtalene, anthracene, a reducing agent like a metal powder (magnesium) and an oxidizer like hexachlorobenzene and/or hexachloroethane.

The technical sector of this invention is that of smoke-producingmethods and ammunition which are designed to produce a smoke screen thatmakes it possible to shield any target by preventing transmission ofinfrared radiance emitted by it in order to make it undetectable to asensor.

At present there exist few publications which discuss ammunitiondesigned to produce smoke that is opaque to infrared radiance. However,the execution of classical smoke-producing ammunition or devices is wellknown. Those ammunition usually include a cylindrical pot inside whichwe place a pyrotechnical composition or tablets of pyrotechnicalcompositions which may or may not have a central channel. For moredetails, we can refer to French Pat. No. 2 249 590 which describes asmoke-producing device of which the emissions are entirely transparentto infrared radiance. This type of composition can generate a whitesmoke by producing zinc chloride or ammonium chloride, carbon beingtransformed into carbonic gas.

The emergence of new surveillance means (thermal cameras) has alteredthe factors in the problem because those means make it possible toidentify a target from its thermal radiance proper in the transparencywindows 3 to 6 μm and 7 to 14 μm. We already suggested the scattering ofaerosols so as to shield the infrared radiance emitted by a target.

Hence, we know the French Pat. Nos. 2 299 617 and 2 309 828 whichdescribe the forming of a liquid aerosol through hydrolysis of titaniumor tin tetrachloride.

We then use a scattering and highly exothermal pyrotechnicalcomposition, of the aluminum or boron/potassium perchlorate type inorder to scatter titanium tetrachloride. However, this kind of aerosolwhich is comprised of hydrosoluble liquid droplets is not at alleffective, it requires water or dampness and it has a very shortlifespan, which is less than 20 s regardless of the volume of thescattering system. Furthermore, this system generates acid, corrodingand toxic compounds.

We also know U.S. Pat. No. 2,396,265 which describes the scattering ofsolid particles from a mineral powder and a vector gas (compressed air,nitrogen, etc.) in order to prevent through scattering the thermalradiance of a target. However we must control the granulometry of theparticles which are contained in the emitted aerosol because only finalgranulometry which comes close to the wave length of the radiance to beshielded is effective. And yet, we have observed that the production ofa solid particle aerosol of which the diameter might be included between1 and 14 μm, does not allow for the elimination of the thermal image ofthe target in an effective way and for a sufficient lapse of time due tosedimenting of the particles which intervenes. The lifespans which areobtained do not exceed 25 seconds.

We also know the French Pat. Nos. 2 294 422 and 2 294 432 which describeinfrared decoys which transmit through combustion of a pyrotechnicalcomposition, a high intensity flame which thus defines a source ofinfrared radiance which can be substituted for the radiance sourcecomprised of the engine of the aircraft in the guidance system of thedevice launched against it. The point is not to emit carbon particles ofa particular size.

The purpose of this invention is to suggest a method and an ammunitionin order to produce a smoke screen that prohibits transmission ofinfrared and visible radiance to completely shield a target for asufficient lapse of time, or 40 to 50 s.

Therefore, the invention concerns a method for shielding visible andinfrared radiance with a wave length included between 0.4 and 14 μm thatis emitted by a target, characterized in that in an initial stage weproduce instantly an initial hot aerosol which masks the target throughthe scattering in the visible spectrum and with its emitter power in theinfrared world, and in a second stage we produce a second aerosol whichcontains mostly hot carbon particles measuring 1 to 14 μm in order toshield essentially through diffraction the thermal image that istransmitted by the target.

According to a particular implementation we generate the first andsecond aerosol from pyrotechnical compositions.

The invention also concerns a smoke-producing pyrotechnical ammunitionfor the implementation of the original method in that it includes a tubewhich is closed at both ends by a cover, at least one of those covers isequipped with one or more orifices, the tube enclosing at least a fastpyrotechnical composition which has a regimen of less than 1 s and acombustion speed which amounts to about 6 mm/s under operating pressure,in order to generate hot gasses with a flow equal at least to 160 g/s soas to shield through saturation the thermal image of the target, and atleast a slow pyrotechnical composition which has a combustion speed ofabout 1 mm/s under operating pressure generating hot carbon particles,each composition equipped with a central channel, ignition means plannedto initiate fast compositions.

The fast composition can be a tablet executed under pressure whichincludes a zinc or zinc oxide, potassium perchlorate, hexachlorobenzeneor hexachloroethane powder and a binding agent comprised of neoprene.

The constituents of the fast composition can be selected according tothe following mass ratios:

31% zinc,

12% zinc oxide,

16% potassium perchlorate,

31% hexachlorobenzene and/or hexachloroethane,

10% neoprene.

The slow composition can be a tablet which is executed under pressureand it includes a compound which generates carbon particles of which thesize is included between about 1 and 14 μm, an oxidoreducing systemwhich reacts to a temperature that exceeds 1000 degrees C. and a bindingagent.

The reducing agent of the composition can be selected among metalpowders especially magnesium; and the oxidizer can be represented byhexachlorobenzene, hexachloroethane or their mixture.

The slow composition can include the following ternary system:

15 to 25 parts in weight of magnesium powder,

50 to 85 parts in weight of hexachlorobenzene or hexachloroethane,

0 to 30 parts in weight of naphtalene.

The ammunition can include five tablets which are piled in the followingorder:

a fast composition tablet,

three successive slow composition tablets,

a fast composition tablet,

and an ignition tablet which is placed on contact with each of the fastcomposition tablets.

Advantageously the diameter of the central channel in the slowcompositions is greater than that of the fast compositions.

One advantage of this invention rests in the fact that by combining twocompositions which emit on the one hand an extremely hot aerosol to maskwith its superior emitting potential the thermal image of the target andon the other hand a solid particle aerosol which preempts throughdiffraction the thermal image of the target one obtains instantly aprotective screen for the target for a lapse of time which is sufficientamount to 40 to 50 s. Furthermore, the high intensity and exothermalcombustion of the fast composition leads within the device to thereduction of the regimen setting of the slow composition as well as toan increase of its combustion speed during the initial operatingseconds. This action makes it possible to increase the flow of emissionof the ammunition and correlatedly to accrue particle concentration inthe cloud of smoke. We therefore avoid a reduction of the aerosoldensity which corresponds to the short period located between theemission end due to the fast composition and the beginning of emissiondue to the slow composition. The result is an improvement ofeffectiveness and regularity in the smoke-producing screen againstinfrared radiance.

As it is already shown in what preceded we are implementing a highlyexothermal composition which has great combustion speed. Thecompositions which meet these criteria are usually highly reducing metalpowder bases for instance zinc or aluminum. This metal powder can beassociated to a metal oxide like zinc oxide. The oxidizer can also behighly exothermal and those of the chlorate or perchlorate kind orperfectly suited without representing a limitation. Potassiumperchlorate makes it possible to obtain excellent results. Therefore thereaction leads to chlorides which can be hydrolysed like zinc oraluminum chlorides. The oxidizer can be associated to saturated carboniccompounds which are partially or completely substituted byelectronegative elements like chlorine or fluoride. As an example wewill mention hexachlorobenzene or hexachloroethane. Obviously, we willimprove the mechanical hold of the tablet by adding a binding agentwhich is not in and of itself a characteristic of the invention. Thebinding agents which are conventionally used in pyrotechnics can beimplemented and we will mention as an illustration neoprene, vinylpolychloride, polyvinyl acetate, vinyl acetochloride, polyurethanes,etc. The respective percentages of constituents can be selectedaccording to the sought goal.

The fast composition emits a smoke which is greyish to white, and it canbe black according to the carbonic compound in use. Hence when we usehexachlorobenzene the smoke which is emitted becomes black. We shouldnote that the fast composition burns completely and leaves no residue.The massic flow is increased and all of the smoke-producing material istransformed into smoke.

According to the invention, we associate to this fast composition a slowcomposition which includes a compound that generates carbon particles inorder to produce through diffraction a screen which is opaque toinfrared radiance from the target. Therefore we can use paraffins,condensed or not benzene compounds, naphtalene and anthracene,phenanthrene and naphtol make it especially possible to obtain goodresults. The oxidoreducing system must supply a combustion temperaturewhich exceeds 1000 degrees C.; the metal powders which are associated tothe classical oxidizers of the nitrate, perchlorate kind can be used.However we prefer, according to the invention, to optimize thepyrotechnical composition that is slow by using a compound whichgenerates carbon particles and which is sufficiently ozidizing to reactwith the reducing agent, non substituted hydrocarbonic compounds. As anexample, the hexachlorobenzene-napthalene couple makes it possible toexecute slow pyrotechnical compositions which generate intense smokethat can mask infrared radiance of a target. Obviously, we can use asubstituted hydrocarbonic compound in conjunction with a classicaloxidizer. As such the binding agent does not represent a characteristicof this composition and it is used to reinforce the mechanical hold ofthe composition. However, we will choose preferably the macromolecularcompounds of the fluoridated kind which participate in the combustionreaction through the intake of highly oxidizing fluoride molecules forinstance vinylidene polyfluoride and also other polymers such as vinylacetochloride copolymer, polystyrene, which is reticulated or not,methyl/styrene methacrilate copolymer and neoprene are adequate. Theproportion of binding agent which is used can amount to 5 to 20 parts inweight not to exceed 25 parts in weight.

In order to prepare the pyrotechnical compositions according to theinvention we can proceed in the following way or in an equivalent way.

First the metal powder is subjected to stoving at about 50 degrees C.for 24 hours. The solid compounds such as perchlorate, hexachlorobenzeneand anthracene are sifted at about 0.5-0.65 mm. Then they are introducedin turn inside the vat of a mixer and mixed for 15 to 30 minutes. Fromthe obtained mixture, we execute tablets which include a central channelunder pressure equal to about 6.10⁵ Pa.

The invention will be better understood when reading the additionaldescription which follows on implementation modes provided as examplesin relation to a plate (FIG. 1) which represents a lengthwise section ofammunition according to the invention.

On the figure, we represented a smoke-producing ammunition 1 which isdesigned to be ejected from a launching tube that is not representedwith a propeller 3 of the known type which is integrated to theammunition. This ammunition includes a tubular envelope 4 made of steelclosed at both ends with two covers 5 and 6. Cover 5, which is in thevicinity of the propeller 3, includes a number of holes or orifices 5adesigned to enable the initiation of the ignition composition 7 duringthe launch. Cover 6 includes a central hole 6a and off-center holes 6b.Those various holes can be obstructed with easily melted mats. Insidethe envelope 4, a fast composition tablet 8 is arranged, with three slowcomposition tablets 9, 10, 11, and a fast composition tablet 12. Anignition composition tablet 13 is placed at the base of the tablet 12and it is used as the ignition relay.

On the figure, we see that the diameter of the central channel 14 of thetablets 9, 10, 11 is greater than that of the slow 8 and 12 due to adifference in combustion speed which exists between the fast and slowcompositions. The central channel is a guide for ignition and itsdiameter depends on the nature of the smoke-producing composition.

As an example, we can execute ammunition with the followingcharacteristics:

diameter of the envelope 80 mm,

height of the envelope 360 mm,

tablets 7 and 13 mass 22 g.

height 8 mm,

outer diameter: φ 50 mm,

diameter of the central hole: φ 18 mm,

tablets 8 and 12: mass 733 g,

height 69 mm,

diameter of a central hole: φ 30 mm.

tablets 9, 10 and 11: mass 388 g,

height 65 mm,

diameter of the central hole: φ 30 mm.

The overall mass of the ammunition is abut 4 kg and it includes 2370 kgin smoke-producing composition which provides an effective shield for 50s.

As stated previously, the ammunition is designed to be launched in orderto insert a screen which is opaque to infrared radiance between a targetand a sensor, To this end, at the time of launch, igniting the propellertakes place for instance with an electric initiator. Under the activityof the propelling bloc, the ammunition is ejected at a distance of 20 to70 meters from the target to be protected. As soon as the launching tubeis out, the tablets 8 and 12 catch on fire with a response time that islower than 1 s by way of tablets 7 and 13 which are initiated themselvesby the propeller. Those tablets burn by emitting a white smoke throughholes 5a, 6a which forms a barrel. Smoke emission on the trajectory,connected to the speed of the regimen setting of the tablets 8 and 12makes it possible to set up an instantaneous protective screen. Theemitted smoke is extremely hot and it represents an aerosol which masksthe target by diffusing in the visible spectrum and with its superioremitting potential to that of the target in the infrared zone. Operatingtime amounts to about 7 or 9 s. After a 3 s delay, the tablets 9, 10, 11are initiated under the combined action of the combustion from theignition tablets and tablets 8 and 12. They emit a cloud of smoke whichis black and which represents an aerosol that basically includes hotcarbon particles of which the size is included between 1 and 14 m thatessentially shield through diffraction the thermal image that is emittedby the target. Time of emission of the ammunition is included between 40and 50 s in the infrared zone and 1 minute in the visible spectrum.

The following examples of fast and slow compositions are provided as anillustration:

FAST COMPOSITION: tablets executed under pressure of about 6.10⁷ Pa.

(1)

31% mass of zinc powder,

12% mass of zinc oxide,

16% mass of potassium perchlorate,

31% mass of hexachloroethane,

10% mass of neoprene binding agent.

(2)

31% mass of zinc powder,

12% mass of zinc oxide,

16% mass of potassium perchlorate,

31% mass of hexachloroethane,

10% mass of neoprene binding agent.

Those compositions display a combustion speed of 1.03 mm/s in open airand 6 mm/s under operating pressure in the ammunition.

The mechanical characteristics are as follows:

Resistance to compression Smc=78.710⁵ Pa

Resistance to extension emc=3.31%.

Flaming temperature: 425 degrees C.

Activating energy: 25 389 Cal/g.

SLOW COMPOSITION: tablets executed under pressure of about 610⁷ Pa.

(1)

20 parts weight of magnesium powder,

80 parts weight of hexachlorobenzene,

10 parts weight of naphthalene,

10 parts weight of binding agent (vinylidene polyfluoride),

(2)

20 parts of magnesium powder,

80 parts of hexachlorobenzene,

10 parts of anthracene,

10 parts of binding agent represented by vinylidene polyfluoride.

(3)

20 parts of magnesium powder,

70 parts of hexachlorobenzene,

10 parts of naphthalene,

5 parts of binding agent represented by neoprene.

(4)

20 parts of magnesium powder,

70 parts of hexachlorobenzene,

10 parts of naphthalene,

10 parts of binding agent represented by vinylidene polyfluoride.

(5)

18.5 parts of magnesium powder,

61.5 parts of hexachloroethane,

30 parts of naphtalene,

20 parts of chlorinated parrafin,

20 parts of binding agent represented by vinylidene polyfluoride.

(6)

20 parts of magnesium powder,

80 parts of hexachlorobenzene,

5 parts of binding agent represented by polyvinyl actate.

(7)

20 parts of magnesium powder,

80 parts of hexachlorobenzene,

20 parts of vinylidene polyfluoride.

Those compositions display combustion speed of 0.57 mm/s in open air and1 mm/s under operating pressure in the ammunition.

The mechanical characteristics are as follows:

maximal constraint under uniaxial compression Smc: 178.10⁵ Pa,

distortion for maximal compression emc=0.87%.

In order to simulate aging, we subject the pyrotechnical compositions torespective temperatures of -40 degrees C. and +51 degrees C. for onemonth and we realize that the variations in their characteristics(combustion speed, mechanical hold, mass loss, size, etc.) are few.

We claim:
 1. A method for shielding radiance emitted by a target in thevisible spectrum and the infrared spectrum at wavelengths between about0.4 and 14 μm comprising:producing a first hot aerosol to shield thetarget primarily through diffusion in the visible spectrum and primarilythrough emission in the infrared zone; producing a second hot aerosolsubstantially comprising hot carbon particles to shield the targetprimarily through diffraction, said hot carbon particles havingdiameters substantially between 1 and 14 μm.
 2. The method according toclaim 1, wherein said first and second aerosols are generated bypyrotechnical compositions.
 3. A smoke-producing pyrotechnicalammunition comprising:a tube closed at both ends by covers, at least oneof said covers having one or more orifices; at least one fastpyrotechnical composition enclosed within said tube having a regimensetting less than about 1 s and a combustion speed of about 6 mm/s underoperating pressure for generating a flow of hot gasses of at least 160g/s to shield primarily through saturation the thermal image of thetarget; at least one slow pyrotechnical composition enclosed within saidtube having a combustion speed of about 1 mm/s under operating pressurefor generating a flow of hot carbon particles to shield primarilythrough diffraction the thermal image of the target; ignition means forigniting said at least one fast composition; and wherein each of saidfast and slow compositions has a central channel formed therein.
 4. Theammunition according to claim 3, wherein said at least one slowcomposition has a regimen setting of about 3 s.
 5. The ammunitionaccording to claim 3, wherein said fast composition comprises zinc, zincoxide, potassium perchlorate, neoprene and at least one substanceselected from the group consisting of hexachlorobenzene andhexachloroethane.
 6. The ammunition according to claim 5, wherein saidfast composition comprises about the following mass percentages of thestated substances:31% zinc; 12% zinc oxide; 17% potassium perchlorate10% neoprene 31% hexachlorobenzene and/or hexachloroethane.
 7. Theammunition according to claim 3, wherein said at least one slowcomposition further comprises a tablet executed under pressure from acompound which generates carbon particles between about 1 and 14 μm insize, an oxidoreducing system which reacts at a temperature exceedingabout 1000° C., and a binding agent.
 8. The ammunition according toclaim 7, wherein said compound for generating carbon particles comprisesat least one substance selected from the group consisting ofhexachloroethane, hexachlorobenzene, napthalene, and anthracene.
 9. Theammunition according to claim 8, wherein the oxidoreducing systemcomprises at least one reducing agent selected from the group consistingof metal powders, and at least one oxidizing agent selected from thegroup consisting of hexachlorobenzene and hexachloroethane.
 10. Anammunition according to claim 9, wherein said slow composition comprisesabout the following portions of the stated substances:15 to 25 parts byweight of zinc powder; 50 and 85 parts by weight of hexachlorobenzeneand/or hexachloroethane; 0 to 30 parts by weight of anthracene.
 11. Theammunition according to claim 10, wherein said fast and slowcompositions and said ignition means are formed into tablets, andwherein said fast and slow composition tablets are disposed along anaxial length of said tube in the following order:a first fastcomposition tablet; three successive slow composition tablets; a secondfast composition tablet; and at least one of said ignition tablets isplaced in contact with each of said fast composition tablets.
 12. Theammunition according to claim 3 wherein the central channel of said slowcomposition has a larger diameter than the central channel of said fastcomposition.